Well, originally it was an FS but the foam deteriorated.  Also, it had a bronze voice coil, therefore the model is FSB.  As to why bronze was used, I can only assume that the reason(s) were similar to those for the aluminum coils used on some models.  However, the density of most common bronze alloys is close to that of copper, 8.9 gm/cm^3 as is resistivity, being near the  1.7e10-8 ohms/meter of copper.  

The variations in both these parameters is not anywhere near aluminum , which has a density of about a third that of copper, 2.7g.cm^3 and a resistivity of 1.5 times that of copper, 2.6e10-8 ohms/meter.  The considerably lighter density of aluminum is probably why it was used for the Super 3 tweeter and some 8 inch units designed for two way systems.  Aluminum coils were also used in the Super12 FS/AL for reasons that baffle me.  The lighter mass of an aluminum coil would be moot once attached to a massive 12 inch diaphragm.











The original cone, coil and spider.  

This coil was salvaged but the other was too knotted.

A closer look at the coil.  Believe it or not, it was salvaged.
I won't speculate on how these fluid marks happened.
It took the duration of a movie to unravel this.
The salvaged coil wire.  The coil form, right piccy, was probably damaged by overdriving in the bass and judging by the lack of evidence of overheating, destruction was immediate.
The making of the annulus ring.  The disk was rough cut from 1/8 inch hardboard.  A screw was used to hold it to the plywood which was clamped to the router table.  Rotating the disc produced a nice circle.
A similar technique was use as above but this time the router bit was lowered and inserted into a hole.  The disk was again rotated but only about half way around. 

  It was the raised at the edge and lowered onto the rotating bit and rotated again about half way,.  This left two spokes to keep the outer and inner discs concentric.  The spokes were removed manually.

The two annulus rings.
The hand wound coil is fixed around the pole piece.  The shims are 0.005" each; blue and orange.  The blue kinda holds the coil in place but can move when the spider and cone are applied, ergo the shim strips to lock it.  This was a temporary assembly as the coil wasn't firmly locked in place.

Red shims were later used, 0.007"

The ring was later drilled with 12 holes as was the frame, the latter being threaded 4-40.

The coil locked to the pole piece.  These coils are underhung, meaning the coil length is the same as the top plate thickness.  This is a bass midrange good to about 300 hz.  It was never intended as a woofer, at least not by today's standards.
Similar drilling and threading of the spider ring and frame was later done.
Here's the spider glued to the coil and held in place by the purple ring.
Almost done.
The finished units.

The idea behind using rings for assembly is to enable removal of the moving system to be replaced by a modified cone; one with damping compound on the back.  I had exceptional results doing that to a pair of 5 inch paper cone midranges.

I have 10 of these cones left and 4 more handwound voice coils.


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